The present invention relates to an extension device which is provided with at least a first tubular member and a second tubular member inserted in the said first tubular member in such a way that the length of its projecting portion is adjustable.
Examples of conventional extension devices include an extension device 1 shown in FIG. 7, which is used as a leg assembly of a tripod.
The extension device 1 shown in FIG. 7 has a first tubular member 2 and a second tubular member 3 inserted in the first tubular member 2 in such a way that the length of its projecting portion is adjustable.
The first tubular member 2 has a first tubular body portion 6. Grooves 4, 4 having an approximately V-shaped cross section are formed integral with the first tubular body portion 6 by press working, extrusion, or by any other appropriate process. The grooves 4, 4 extend in the axial direction of the first tubular body portion 6 so that the V-shaped cross section protrudes inward. The second tubular member 3 has a second tubular body portion 7. Grooves 5, 5 extending in the axial direction of the second tubular body portion 7 and having an approximately V-shaped cross section protruding inward are formed integral with the second tubular body portion 7 by press working, extrusion, or by any other appropriate process.
The extension device 1 is designed such that engagement of each groove 4 of the first tubular body portion 6 with the corresponding groove 5 of the second tubular body portion 7 prevents rotation of the second tubular member 3 with respect to the first tubular member 2.
However, the conventional extension device 1 shown in FIG. 7 presents a problem in that the wall of the first tubular body portion 6 must have a certain thickness. Otherwise, a relatively great rotational force or other similar stress applied to the second tubular member 3 may deform the first tubular body portion 6, resulting in undesirable rotation of the second tubular member 3 with respect to the first tubular member 2.
In order to solve the above problem, an object of the present invention is to provide an extension device which enables the appropriate prevention of undesirable rotation of the second tubular member 3 with respect to the first tubular member 2.
An extension device according to the present invention includes at least a first tubular member and a second tubular member, which is so inserted inside the first tubular member that the length of its projecting portion is adjustable, wherein the first tubular member includes a first tubular body portion and one or more protruding portions, each of which extends from one axial end to the other axial end of the first tubular body portion in such a way as to protrude inward from the inner surface of the first tubular body portion so that no recess is formed on the outer surface of the first tubular body portion that corresponds to the location of the protruding portion; and the second tubular member includes a second tubular body portion, which is smaller in diameter than the first tubular body portion, and a rotation prevention portion attached to or formed integral with the second tubular body portion, the rotation prevention portion adapted to come into contact with the protruding portion(s) and thereby prevent the second tubular member from rotating circumferentially relative to the first tubular member.
The features of the invention described above permit the first tubular body portion to have a relatively thin wall without the risk of the first tubular body portion being undesirably deformed when a relatively great rotational force or other similar stress is applied to the second tubular member. Another benefit of the present invention lies in its capability of appropriately preventing undesired rotation of the second tubular member relative to the first tubular member.
An extension device according to another feature of the present invention includes at least a first tubular member and a second tubular member, which is so inserted inside the first tubular member that the length of its projecting portion is adjustable, wherein the first tubular member includes a first tubular body portion and one or more protruding portions, each of which extends from one axial end to the other axial end of the first tubular body portion in such a way as to protrude inward from the inner surface of the first tubular body portion so that no recess is formed on the outer surface of the first tubular body portion that corresponds to the location of the protruding portion; and the second tubular member includes a second tubular body portion, which is smaller in diameter than the first tubular body portion, and a rotation prevention portion attached to or formed on the outer surface of the second tubular body portion as an integral body therewith, the rotation prevention portion rising outward from the outer surface of the second tubular body portion and adapted to come into contact with the protruding portion(s), thereby preventing the second tubular member from rotating circumferentially relative to the first tubular member; and the extent to which each protruding portion protrudes is nearly the same as the extent to which the rotation prevention portion rises from the outer surface of the second tubular body portion.
The feature of the invention described above permits the first tubular body portion to have a relatively thin wall without the risk of the first tubular body portion being undesirably deformed when a relatively great rotational force or other similar stress is applied to the second tubular member. Another benefit of the present invention lies in its capability of appropriately preventing undesired rotation of the second tubular member relative to the first tubular member. Furthermore, as the extent to which each protruding portion protrudes is nearly the same as the extent to which the rotation prevention portion rises from the outer surface of the second tubular body portion, the difference in diameter between tubular members that are connected to each other can be reduced compared with cases where the protruding extent of the protruding portions exceeds the thickness (i.e. the height) of the rotation prevention portion.
An extension device according to yet another feature of the present invention is characterized in that the first tubular member is provided with a protruding stopper portion, which extends around nearly the entire inner surface of an axial end of the first tubular body portion except for the portion(s) where the protruding portion(s) are located so as to protrude inward from the inner surface of the first tubular body portion, and that the rotation prevention portion of the second tubular member is adapted to come into contact with the protruding stopper portion so as to function as a stopper for preventing the second tubular member from dropping off the first tubular member.
As the rotation prevention portion of the second tubular member has a function as a stopper, the extension device according to the invention described above is of a simple structure and easier to be assembled, compared with a structure that calls for forming a stopper as a separate body.
An extension device according to yet another feature of the present invention is characterized in that a pair of receiving surfaces are formed along the two axially extending side faces of each protruding portion of the first tubular member and that the rotation prevention portion of the second tubular member includes one-direction rotation preventing contact surfaces and other-direction rotation preventing contact surfaces, each one-direction rotation preventing contact surface adapted to come into surface contact with one of the two receiving surfaces of the corresponding protruding portion, and each other-direction rotation preventing contact surface adapted to come into surface contact with the other receiving surface of the corresponding protruding portion.
Because of surface contact of each one-direction rotation preventing contact surface of the rotation prevention portion with one of the two receiving surfaces of the corresponding protruding portion and surface contact of each other-direction rotation preventing contact surface with the other receiving surface of the corresponding protruding portion, the extension device having this feature of the invention ensures more appropriate prevention of rotation of the second tubular member relative to the first tubular member.